The present invention relates to processed for the catalytic cracking of heavy petroleum fractions so as to produce lighter hydrocarbon products such as fuel products. More particularly, the invention relates to a process for the catalytic cracking of heavy petroleum fractions which utilizes a catalyst comprising (a) a layered metal oxide of the titanometallate type intercalated with an interspathic polymeric chalcogenide, e.g., polymeric silica and, optionally (b) a large pore porous crystalline silicate component such as a large pore zeolite.
The conversion of various petroleum fractions by catalytic cracking so as to reduce the molecular weight of the contained hydrocarbons is well known in the art. In such a conversion, a petroleum fraction based feedstock is brought into contact with a particulate catalyst under appropriate condition such as elevated temperatures (e.g., at least 400.degree. C.) so as to convert the feedstock into a variety of products which, upon fractionation and the like, yield one or more of gas, gasoline, light cycle gas oil and heavy cycle gas oil. Much of the petroleum refining industry utilizes a fluid bed catalytic cracking reactor for this purpose. Such a reactor typically comprises a thermally balanced assembly of apparatus comprising the reactor vessel containing a mixture of regenerated catalyst and the feedstock and a regenerator vessel wherein spent catalyst is regenerated. As the feedstock is converted in the reactor vessel over the catalyst, coke is simultaneously formed on the catalyst, thereby deactivating the same. The deactivated (spent) catalyst is removed from the reactor vessel and then conducted to a regenerator vessel, where coke is burned off the catalyst with air, thereby regenerating the catalyst which is then recycled to the reactor.
Conventional catalysts used in catalytic cracking are, for example, those containing silica, silica-alumina or mixtures thereof. Particularly useful catalysts are acidic zeolites, preferably low coke-producing crystalline zeolite cracking catalysts comprising faujasite, and other zeolites known in the art. Typically, the catalyst is of fine particles having an average size of about 20 to 100 microns.
While the above catalysts have been generally satisfactory for their intended use in catalytic cracking operations, it has now been found that enhanced catalytic cracking can be achieved by utilizing a catalyst containing (a) a layered metal oxide of the titanometallate-type intercalated with an interspathic polymeric chalcogenide, and optionally, (b) a large pore porous crystalline silicate component such as a zeolite material.
More particularly, the titanometallate-type layered metal oxide product comprises a layered metal oxide and pillars of a chalcogenide of at least one element selected from Groups IB, IIB, IIIA, IIIB, IVA, IVB, VA, VB, VIA, VIIA and VIIIA of the Periodic Table of the Elements (Fisher Scientific Co. Cat. No. 5-702-10, 1978) separating the layers of the metal oxide, wherein each layer of the metal oxide has the general formula EQU [M.sub.x [].sub.y Z.sub.2-(x+y) O.sub.4 ].sup.q-
wherein M is at least one metal of valence n wherein n is an integer between 0 and 7 and preferably is 2 or 3, []represents a vacancy site, Z is a tetravalent metal, preferably titanium, and wherein EQU q=4y-x(n-4) and preferably is 0.6-0.9, O&lt;x+y&lt;2
The metal oxide product contains about 0.5 to about 20 weight percent of said element M, preferably about 1 to 10 weight percent.
The intercalated titanometallate-type layered metal oxide product employed in the present invention comprises a layered titanometallate-type layered metal oxide and interspathic polymeric chalcogenide of at least one element, separating the layers of the metal oxide. Preferably, such materials after pillaring are thermally stable, i.e., capable of withstanding calcination at a temperature of about 450.degree. C. for at least 2 hours without significant reduction (e.g., not greater than 10 or 20%) in the spacing between the layers.
It is to be appreciated that the term "layered" metal oxide is used herein in its commonly accepted sense to refer to a material which comprises a plurality of separate metal oxide layers which are capable of being physically displaced away from one another such that the spacing between adjacent layers is increased. Such displacement can be measured by X-ray diffraction techniques and/or by density measurements.
For purposes of the present invention the term "chalcogenide" includes members of the group consisting of oxides, sulfides, selenides, tellurides, and polonides of elements other than those of Group VIB of the Periodic Table of the Elements (Fisher Scientific Co. Cat. No. 5-702-10, 1978). Oxides are particularly preferred as the interspathic polymeric chalcogenide. For present purposes, polymeric chalcogenides are considered to include chalcogenides of two or more repeating units, preferably three or more repeating units, say four or more or even five or more repeating units. The extent of polymerization of the interspathic polymeric chalcogenide is believed to affect the ultimate interlayer separation of the titanometallate-type layered metal oxide product.
In preparing the intercalated layered titanometallate-type layered metal oxide product material used in the catalyst composition, the interlayer separation of the layered titanometallate-type layered metal oxide material can be tailored by careful selection of the "propping" agent used to separate the layers prior to or during treatment with the interspathic polymeric chalcogenide precursors which are eventually converted to the thermally stable polymeric chalcogenide "pillars". Indeed, a wide range of interlayer separations can be achieved in preparing layered materials of the present invention. Interlayer distances can range anywhere from 2 to 30 angstroms or more, say, e.g., greater than 5, 10, 15 or 20 angstroms, depending largely on the type of "propping" agent used as well as the layered chalcogenide being treated. The titanometallate-type layered metal oxide material when intercalated contains an interspathic polymeric chalcogenide of at least one element selected from Groups IB, IIB, IIIA, IIIB, IVA, IV, VA, VB, VIA, VIIA, and VIIIA of the Periodic Table of the Elements (Fisher Scientific Co. Cat. No. 5-702-10, 1978). For example, the intercalated titanometallate-type layered metal oxide can be prepared by treating the titanometallate-type layered metal oxide which contains ion exchange sites having interspathic cations associated therewith, with an organic compound which is a cationic species or capable of forming a cationic species, to effect exchange with said interspathic cations. An electrically neutral compound capable of conversion to the interspathic polymeric chalcogenide is provided between the layers of the treated layered metal oxide. The compound is then converted to the interspathic polymeric chalcogenide to form the intercalated titanometallate-type layered metal oxide product.
The titanometallate-type layered metal oxide starting material contains ion exchange sites having interspathic cations associated therewith. Such interspathic cations may include hydrogen ion, hydronium ion and alkali metal cation. The starting material is treated with a "propping" agent comprising a source of organic cation such as organoammonium, which may include the cation itself, in order to effect an exchange of the interspathic cations resulting in the layers of the starting material being propped apart. Suitable alkylammonium cations can include n-dodecylammonium, n-heptylammonium, n-hexylammonium and n-propylammonium. The source of organic cation in those instances where the interspathic cations include hydrogen or hydronium ions may include a neutral compound such as an organic amine which is converted to a cationic analogue during the "propping" treatment. The organic cation should be capable of displacing or supplanting the original interspathic cations. In some instances, it may be desirable to remove excess propping agent which is not electrostatically bound within the layered starting material in order to permit the addition of greater amounts of polymeric chalcogenide precursor. Such removal may be effected by washing out the propping agent with a material which is soluble with said propping agent. The foregoing treatment can result in the formation of a titanometallate-type layered metal oxide of enhanced interlayer separation depending upon the size of the organic cation introduced. Contact of the layered metal oxide with the propping agent may be conducted in aqueous medium so that water is trapped between the layers of the "propped" metal oxide.
After the ion exchange, the organic-"propped" species is treated with a compound capable of forming the above-described polymeric chalcogenide. Preferably, such compounds are capable of forming the polymeric chalcogenide upon hydrolysis or other polymerizing reactions. Hydrolyzable compounds are well-suited as such compounds. It is preferred that the organic cation deposited between the layers is capable of being removed from the layered oxide material without substantial disturbance or removal of the interspathic polymeric chalcogenide. For example, organic cations such as n-octylammonium may be removed by exposure to elevated temperatures, e.g., calcination in nitrogen or air, or chemical oxidation conditions, preferably after the interspathic polymeric chalcogenide precursor has been converted to the polymeric chalcogenide in order to form the layered material product employed in the present invention.
The polymeric chalcogenide precursor-containing product can be exposed to suitable conversion conditions, such as hydrolysis and/or calcination to form the pillared titanometallate-type layered metal oxide material for the present invention. The hydrolysis step may be carried out by any suitable method, for example, by utilizing interspathic water already present in organic-"propped" titanometallate-type layered metal oxide material. Because of the effect of interspathic water on hydrolysis, the extent of hydrolysis may be modified by varying the extent to which the organic-"propped" species is dried prior to addition of the polymeric chalcogenide precursor. As noted earlier, the product after conversion to the polymeric chalcogenide form may be exposed to conditions which remove organic compounds such as the organic cation propping agents, e.g., exposure to elevated temperatures such as those encountered by calcining in air or nitrogen.
In one embodiment the titanometallate-type layered metal oxide, exclusive of its interspathic polymeric chalcogenide, has the empirical formula EQU Cs.sub.4y ([].sub.y Ti.sub.2-y)O.sub.4
The catalyst composition of the present invention generally contains between about 5 to 95, preferably between about 10 to 20, weight percent of said intercalated titanometallate-type layered metal oxide and about 5 to 95, preferably about 80 to 90, weight percent of a shape-selective porous crystalline silicate material, e.g., Zeolite Y.
In a particularly useful composition for the present invention, the titanometallate-type layered metal oxide has the following additional limitations: n=3, M is Ga.sup.3+, Z is Ti.sup.4+, y=0 and the interspathic polymeric chalcogenide includes polymeric silica. Another useful composition for the present invention has a layered titanometallate-type layered metal oxide component wherein n=2, M is Zn.sup.2+, Z is Ti.sup.4+, y=0 and said interspathic polymeric chalcogenide comprises polymeric silica.
The titanometallate-type layered metal oxide may comprise about 15 to 40 weight percent of the composition of the present invention while the crystalline silicate material may comprise about 60 to 85 weight percent of said composition. The composition may also comprise an inorganic oxide binder, e.g., alumina.
Certain titanometallate-type layered metal oxides employed in the present invention are described as well as their method of preparation in U.S. application Ser. No. 879,787, filed June 27, 1986, the entire contents of which are incorporated herein by reference. Such materials are layered titanometallates comprising interspathic polymeric chalcogenide having the general formula A.sub.x (M.sub.x/n Ti.sub.2-x/n)O.sub.4, exclusive of the interspathic polymeric chalcogenide, where A is a monovalent cation and n=1 or 2 provided that: where n=1, 0 is less than x is less than 2 and M is a trivalent cation; where n=2, 0 is less than x is less than 4 and M is a divalent cation.
The titanometallate-type layered metal oxides employed in the present invention are described in PCT/US87/01444, filed June 11, 1987. These materials are more broadly defined as a layered product comprising a layered metal oxide and pillars of an oxide of at least one element selected from Groups IB, IIB, IIIA, IIIB, IVA, IVB, VA, VB, VIA, VIIA and VIIIA of the Periodic Table of the Elements (Fisher Scientific Co. Cat. No. 5-702-10, 1978) separating the layers of the metal oxide, wherein each layer of the metal oxide has the general formula: EQU [M.sub.x [].sub.y Z.sub.2-(x+y) O.sub.4.sup.]q-
wherein M is at least one metal of valence n wherein n is an integer between 0 and 7 and preferably is 2 or 3, [] represents a vacancy site, Z is a tetravalent metal, preferably titanium, and wherein EQU q=4y-x(n-4) and preferably is 0.6-0.9, O&lt;x+y&lt;2
The layered intercalated product described in the preceding paragraph can be prepared by a method which comprises the steps of starting with said layered metal oxide and physically separating the layers thereof by introducing an organic cationic species between the layers at interlayer anionic sites associated with the layered oxide, introducing between the separated layers of the layered oxide a compound capable of conversion to an oxide and then converting said compound to the oxide to form oxide pillars separating adjacent layers of the layered oxide.
The pillared titanometallate-type layered metal oxide products can have a relatively high interplanar distance (d-spacing), e.g., greater than about 10 angstroms and preferably greater than 20 angstroms up to and even exceeding 30 angstroms. These materials are capable of being exposed to severe conditions such as those encountered in calcining, e.g., at temperatures of about 450.degree. C. for about two or more hours, e.g., four hours, in nitrogen or air, without significant decrease, say, e.g., less than about 10%, in interlayer distance. Furthermore, such pillared oxides can be prepared without the severe dilution often necessary to introduce the interspathic material in prior art techniques of pillaring. Finally, the size of interspathic oxide contained within the final product can be greatly varied because the oxide precursor species is introduced in an electrically neutral form such that the amount of interspathic material incorporated within the titanometallate-type layered metal oxide is not dependent upon the charge density of the original layered oxide. Charge density should be taken into consideration in determining the suitability of the cationic species introduced between the layers in the procedure used to prop open the layers prior to pillaring.
The unpillared titanometallate-type layered metal oxide starting material contains anionic sites having interspathic cations associated therewith. Such interspathic cations may include hydrogen ion, hydronium ion and alkali metal cation.
More specifically, each layer of the titanometallate-type layered metal oxide starting material has the general formula EQU [M.sub.x [].sub.y Z.sub.2-(x+y) O.sub.4 ].sup.q-
wherein M is at least one metal of valence n wherein n is an integer between 0 and 7 and preferably is 2 or 3, [] represents a vacancy site, Z is a tetravalent metal, preferably titanium, and wherein EQU q=4y-x(n-4) and preferably is 0.6-0.9, O&lt;x+y&lt;2
Interposed between the layers of the oxide will be charge-balancing cations A of charge m wherein m is an integer between 1 and 3, preferably 1. Preferably A is a large alkali metal cation selected from the group consisting of Cs, Rb and K and M is a divalent or trivalent metal cation selected from at least one Mg, Sc, Mn, Fe, Cr, Ni, Cu, Zn, In, Ga and Al. For example, M can be both In and Ga. Structurally, these metal oxides are believed to consist of layers of (M.sub.x [].sub.y Z.sub.1-x-y)O.sub.6 octahedra which are trans edge-shared in one dimension and cis edge-shared in the second dimension forming double octahedral layers which are separated by cations in the third dimension. These materials can be prepared by high temperature fusion of a mixture of (1) metal oxide, (2) alkali metal carbonate or nitrate and (3) tetravalent metal dioxide, e.g., titanium dioxide or by fusion of a mixture of alkali metallate and tetravalent metal dioxide. Such fusion can be carried out in air in ceramic crucibles at temperatures ranging between 600.degree. to 1100.degree. C. after the reagents have been ground to a homogeneous mixture. The resulting product is ground to 20 to 250 mesh prior to the organic swelling and polymeric oxide intercalation steps.
Further description of layered titanometallate starting materials and their methods of preparation can be found in the following references:
Reid, A. F.; Mumme, W. G.; Wadsley, A. D. Acta Cryst. (1968), B24, 1228; Groult, D.; Mercy, C.; Raveau, B. J. Solid State Chem. 1980, 32 289; England, W. A.; Burkett, J. E.; Goodenough, J. B.; Wiseman, P.J. J. Solid State Chem. 1983, 49 300.
Use of these layered metal oxides as the layered starting material permits inclusion of different metal atoms into the layered starting material being treated which allows potential catalytically active sites to be incorporated in the stable layer itself. Moreover, variable amounts of metal atoms may be added to provide a catalyst with optimum activity for a particular process. Furthermore, the infinite trans-edge shared layer structure of the titanometallate-type layered metal oxides instead of the sheared 3-block structure of, for example Na.sub.2 Ti.sub.3 O.sub.7, may reduce or eliminate shearing of the layers as a possible mechanism for thermal or hydrothermal decomposition of the calcined intercalated material. These titanometallate-type materials may possess even greater thermal stability than silicotitanate molecular sieves. In addition, the variable charge density on the oxide layer possible for these layered metal oxides due to the various oxidation states of metal oxides, the incorporated metal atom and the varying stoichiometry of the materials, may allow variation in the amount of the organic cationic species which can be exchanged into the material. This, in turn, permits variation of the ultimate concentration of the oxide pillars between the layers of the final product.
The titanometallate-type layered metal oxide starting material is initially treated with a "propping" agent comprising a source of organic cation, such as organoammonium cation, in order to effect an exchange of the interspathic cations resulting in the layers of the starting material being propped apart. Suitable organoammonium cations include n-dodecylammonium, n-octylammonium, n-heptylammonium, n-hexylammonium and n-propylammonium. During this propping or swelling step it is important to maintain a low hydrogen ion concentration to prevent decomposition of the titanometallate-type structure as well as to prevent preferential exchange of hydrogen ion over the propping agent. A pH range of 6 to 10, preferably 7 to 8.5 is generally employed during treatment with the propping agent. After this treatment, it has been found advantageous to wash out excess propping agent using a suitable propping agent-soluble reagent followed by washing with water. For example, n-octylamine is soluble in ethanol and hence ethanol is suitable for use with an n-octylamine propping agent. Such washing permits greater incorporation of the oxide pillar precursor in the layered metal oxide. The water treatment allows penetration of water into the interlayer spaces which assists in subsequent hydrolysis of the oxide pillar precursor.
Insertion of the organic cation between the adjoining layers serve to physically separate the layers in such a way as to make the layered material receptive to the interlayer addition of an electrically neutral, hydrolyzable, polymeric oxide precursor. In particular, alkylammonium cations have been found useful in the present invention. Thus C.sub.3 and larger alkylammonium, e.g., n-octylammonium, cations are readily incorporated within the interlayer spaces of the layered metal oxide serving to prop open the layers in such a way as to allow incorporation of the polymeric oxide precursor. The extent of the interlayer spacing can be controlled by the size of the organoammonium ion employed so that use of the n-propylammonium cation can achieve an interlayer spacing of 2 to 5 angstroms whereas to achieve an interlayer spacing of 10 to 20 angstroms an n-octylammonium cation or a cation of equivalent length is required. Indeed, the size and shape of the organic cation can affect whether or not it can be incorporated within the layered structure at all. For example, bulky cations such as tetrapropylammonium are generally undesirable for use in the present method while n-alkyl ammonium cations such as those derived from n-alkyl primary amines R.sub.3 R'N.sup.+ cations where R is methyl or ethyl and R' is an n-alkyl group with at least 5 carbon atoms, are preferred. Preferably treatment with the organic cationic species is conducted in aqueous media so that water is then available to hydrolyze the electrically neutral, hydrolyzable polymeric chalcogenide precursor subsequently introduced into the "propped" product.
After the ion exchange, the organic-"propped" species is treated with a compound capable of conversion, preferably by hydrolysis, to pillars of an oxide, preferably to a polymeric oxide. Where the treatment involves hydrolysis, this may be carried out using the water already present in organic-"propped" material. In this case, the extent of hydrolysis may be modified by varying the extent to which the organic-"propped" species is dried prior to addition of the polymeric oxide precursor.
It is preferred that the organic cation deposited between the layers be capable of being removed from the pillared material without substantial disturbance or removal of the interspathic polymeric oxide. For example, organic cations such as n-octylammonium may be removed by exposure to elevated temperatures, e.g., calcination, in nitrogen or air, or by chemical oxidation preferably after the interspathic polymeric oxide precursor has been converted to the polymeric oxide pillars in order to form the titanometallate-type layered metal oxide product employed in the present invention.
Interspathic chalcogenide pillars are then formed between the layers of the propped or swollen layered metal oxide starting material and may include a chalcogenide, preferably a polymeric chalcogenide, of zirconium or titanium or more preferably of a element selected from Group IVB of the Periodic Table (Fisher Scientific Company Cat. No. 5-702-10, 1978), other than carbon, i.e., silicon, germanium, tin and lead. Other suitable chalcogenides include those of Group VA, e.g., V, Nb, and Ta, those of Group IIA, e.g., Mg or those of Group IIIB, e.g., B. Most preferably, the pillars include polymeric silica. In addition, the chalcogenide pillars may include an element which provides catalytically active acid sites in the pillars, preferably aluminum.
The chalcogenide pillars are formed from a precursor material which is preferably introduced between the layers of the organic "propped" species as a cationic, or more preferably, electrically neutral hydrolyzable compound of the desired elements, e.g., those of group IVB. The precursor material is preferably an organometallic compound which is a liquid under ambient conditions. In particular, hydrolyzable compounds, e.g., alkoxides, of the desired elements of the pillars are utilized as the precursors. Suitable polymeric silica precursor materials include tetraalkylsilicates, e.g., tetrapropylorthosilicate, tetramethylorthosilicate and, most preferably, tetraethylorthosilicate. Where the pillars are also required to include a different polymeric metal oxide, e.g., alumina or titania, a hydrolyzable compound of said metal can be contacted with the organic "propped" species before, after or simultaneously with the contacting of the propped titanometallate with the silicon compound. Preferably, the hydrolyzable aluminum compound employed is an aluminum alkoxide, e.g., aluminum isopropoxide. If the pillars are to include titania, a hydrolyzable titanium compound such as titanium alkoxide, e.g., titanium isopropoxide, may be used. In addition, the chalcogenide precursor may contain zeolite precursors such that exposure to conversion conditions results in the formation of interspathic zeolite material as at least part of the chalcogenide pillars. Pillars of polymeric silica and polymeric alumina or polymeric silica and polymeric titania are particularly preferred.
After hydrolysis to produce the chalcogenide pillars and calcination to remove the organic propping agent, the final pillared product may contain residual exchangeable cations. Such residual cations in the layered material can be ion exchanged by known methods with other cationic species to provide or alter the catalytic activity of the pillared product. Suitable replacement cations include cesium, cerium, cobalt, nickel, copper, zinc, manganese, platinum, lanthanum, aluminum, ammonium, hydronium and mixtures thereof.
The products of the present invention, especially when calcined, exhibit high surface area, e.g., greater than 200, 300, 400 or even 600 m.sup.2 /g, and thermal and hydrothermal stability making them highly useful as catalysts or catalytic supports, for hydrocarbon conversion processes for example, cracking and hydrocracking.
In addition to pillared titanometallate-type layered metal oxide materials, the catalyst used in the process of the present invention may optionally include a porous crystalline silicate component, preferably zeolite materials and, most preferably, large pore zeolites having a Constraint Index less than about 2, as described hereinafter. For purposes of this invention, the term "zeolite" is meant to represent the class of porotectosilicates, i.e., porous crystalline silicates, that contain silicon and oxygen atoms as the major components. Other components may be present in minor amounts, usually less that 14 mole %, and preferably less than 4 mole %. These components include aluminum, gallium, iron, boron and the like, with aluminum being preferred, and used herein for illustration purposes. The minor components may be present separately or in mixtures in the catalyst. They may also be present intrinsically in the structure of the catalyst.
A convenient measure of the extent to which a zeolite provides control to molecules of varying sizes to its internal structure is the Constraint Index of the porous crystalline silicate. Porous crystalline silicates which provide a highly restricted access to and agrees from its internal structure have a high value for the Constraint Index, and zeolites of this kind usually have pores of small size, e.g., less than 5 angstroms. On the other hand, porous crystalline silicates which provide relatively free access to the internal porous crystalline silicate structure have a low value for the Constraint Index, and usually pores of large size, e.g. greater than 7 angstroms. The method by which Constraint Index is determined is described fully in U.S. Pat. No. 4,016,218, incorporated herein by reference for details of the method.
Constraint Index (CI) values for some typical large pore materials are:
______________________________________ CI (at test temperature) ______________________________________ ZSM-4 0.5 (316 .degree. C.) ZSM-12 2.3 (316.degree. C.) ZSM-20 0.5 (371.degree. C.) ZSM-38 2 (510.degree. C.) ZSM-50 2.1 (427.degree. C.) TEA Mordenite 0.4 (316.degree. C.) Mordenite 0.5 (316.degree. C.) REY 0.4 (316.degree. C.) Amorphous Silica-alumina 0.6 (538.degree. C.) Dealuminized Y 0.5 (510.degree. C.) Zeolite Beta 0.6-2.0 (316.degree. C.-399.degree. C.) ______________________________________
The above-described Constraint Index is an important and even critical definition of those porous crystalline silicates which are useful in the instant invention. The very nature of this parameter and the recited technique by which it is determined, however, admit of the possibility that a given porous crystalline silicate can be tested under somewhat different conditions and thereby exhibit different Constraint Indices Constraint Index seems to vary somewhat with severity of operations (conversion) and the presence or absence of binders. Likewise, other variables, such as crystal size of the zeolite, the presence of occluded comtaminants, etc., may affect the Constraint Index. Therefore, it will be appreciated that it may be possible to so select test conditions, e.g., temperature, as to establish more than one value for the Constraint Index of a particular porous crystalline silicate. This explains the range of Constraint Indices for some zeolites, such as zeolite beta.
It is to realized that while the above CI values typically characterize the specified porous crystalline silicates, such values are the cumulative result of several variables useful in the determination and calculation thereof. Thus, for a given zeolite exhibiting a CI value of about 2 or less, depending on the temperature employed during the test method within the range of 290.degree. C. to about 538.degree. C., with accompanying conversion between 10% and 60%, the CI may vary. Likewise, other variables such as the crystal size of the porous crystalline silicate, the presence of possibly occluded contaminants and binders intimately combined with the zeolite may affect the CI. It will accordingly be understood to those skilled in the art that the CI, as utilized herein, while affording a highly useful means for characterizing the porous crystalline silicates of interest is approximate, taking into consideration the manner of its determination, with the possibility, in some instances, of compounding variable extremes. However, in all instances, at a temperature within the above-specified range of 290.degree. C. to about 538.degree. C., the CI will have a value for any given porous crystalline silicate of interest herein of about 2 or less, preferably about 1 or less.
The large pore zeolites, i.e., those zeolites having a Constraint Index of about 2 or less, are well known to the art and have a pore size sufficiently large to admit the vast majority of components normally found in a feed chargestock. The zeolites are generally stated to have a pore size in excess of 7 angstroms and are represented by zeolites having the structure of, e.g., zeolite beta, Zeolite Y, Zeolite X, Ultrastable Y (USY), Dealuminized Y (Deal Y), REY, L, Mordenite, TEA Mordenite, UHP-Y, ZSM-4, ZSM-12, ZSM-18, ZSM-20, ZSM-38, ZSM-50, LZ-210, LZ-210-M, LZ-210-T, and LZ-210-A. A zeolite well known in the art and useful in the present invention is faujasite. The ZSM-20 zeolite resembles faujasite in certain aspects of structure, but has a notably higher silica/alumina ratio than faujasite, as does Deal Y.
Some of these large pore zeolites are more particularly described in U.S. Pat. Nos. 3,308,069 and Reissue 28,341 (zeolite beta); 3,923,639 (ZSM-4); 3,832,449 (ZSM-12); 3,950,496 (ZSM-18); 3,972,983 (ZSM-20); 4,640,849 (ZSM-50); 3,293,192 and 3,449,070 (USY); 3,442,795 (Deal Y); 4,401,556 (UHP-Y) and 4,534,853 (LZ-210, LZ-210-M, LZ-210-T, and LZ-2l0A) respectively, the entire contents of which are incorporated by reference.
As a general rule, the process of the present invention can be utilized with any conventional catalytic cracking unit such as a conventional moving bed reactor or a fluid bed catalytic cracking reactor (FCC unit). In a typical FCC unit, hot catalyst of about 640.degree. to 730.degree. C. is mixed with relatively cold oil feedstock at about 105.degree. to 390.degree. C. The catalyst is the heat transfer medium for vaporizing and superheating the oil feedstock to a temperature suitable for the desired cracking reaction (500.degree.-560.degree. C.). Additional details as to the construction and operation of fluidized catalytic cracking are disclosed in U.S. Pat. Nos. 3,152,065 (Sharp et al.); 3,261,776 (Banman et al); 3,654,140 (Griffel et al.); 3,812,029 (Snyder); 4,093,537 (Gross et al.); 4,118,337 (Gross et al.); 4,118,338 (Gross et al.); 4,218,306 (Gross et al.); 4,444,722 (Owen); 4,459,203 (Beech et al.); 4,578,183 (Chou et al.); as well as in Venuto et al., Fluid Catalytic Cracking With Zeolite Catalysts, Marcel Dekker, Inc. (1979). The entire contents of all of the above patents and publication are incorporated herein by reference in their entirety.
The process of the invention can be utilized with any conventionally-used catalytic cracking feeds including naphthas, gas oils, vacuum gas oils, residual oils, light and heavy distillates and synthetic fuels. The process is particularly adaptable for the selective production of gasoline range materials, especially from the heavier feeds such as residuals due to the relatively large spacing between the layers of the metal oxide catalyst. With the process of the present invention for catalytic cracking, increased yield of gasoline results as compared with the use of conventional cracking catalysts with the increased gasoline yield at the expense of gas make. Furthermore, the process is capable of handling resins where the catalyst preferentially converts the heaviest components.